(a) Field of the Invention
The present invention relates to a process for catalytically converting organic compounds, particularly to a process wherein a catalyst which loses little activity on contact with steam is used. Useful organic compounds are obtained efficiently by applying the process to various catalytic conversions of organic compounds wherein exposure of catalysts to steam occurs, for example, during the catalytic reactions or regeneration of the catalysts.
(b) Description of the Related Art
Zeolite catalysts show activity in various catalytic conversions of organic compounds and are therefore of great industrial importance. There are various zeolites with various structures and compositions, which have been widely used as catalysts or catalyst ingredients in various catalytic conversions of organic compounds. Among these zeolites of various structures and compositions, recently MFI type zeolites with high silica contents represented by ZSM-5 zeolites have become of interest since they have generally exhibited higher activity, higher selectivity and longer lifetimes in various reactions of organic compounds than those exhibited by other zeolites, including A type, X type and Y type zeolites and mordenite.
Many of the conventional zeolites however show insufficient wet heat resistance, which results in a significant disadvantage of easy lowering of catalytic activity on exposure to steam at high temperature, for example, during catalytic reactions or regeneration. MFI type zeolites with relatively high silica contents, such as ZSM-5, have the same disadvantage so far as those conventionally used and reported teach. Therefore, the lowering of catalytic activity due to exposure to steam has been a serious problem for many methods of catalytically converting organic compounds wherein zeolite catalysts inevitably came into contact with steam at high temperature. The contact between catalysts and steam at high temperature occurs, for example, in reactions wherein formation of an atmosphere of steam is accompanied, including dehydration or conversion of alcohols (e.g. MTG process), reactions accompanying generation of water, such as CO/H.sub.2 reactions, reactions using water as a reaction material, such as hydration of olefins, and reactions requiring the presence of water or water-generating ingredients. It should be noted that an atmosphere of steam is also generated during regeneration or pretreatment of catalysts. Even in reactions generating no atmosphere of steam during the reactions, such as catalytic petroleum cracking and conversion of paraffins or olefins, the catalysts are generally regenerated with regeneration gases containing steam to remove carbonaceous matters deposited on the catalysts during the reaction, and come into contact with an atmosphere of a hot steam during the regeneration. This means that a great many processes of catalytically converting organic compounds involve the problem of the lowering of catalytic activity due to such an action of steam.
Further, recently galloaluminosilicates have attracted special interest because of their high catalytic activity exhibited in various catalytic conversions of hydrocarbons, such as aromatization of paraffins or olefins. However, in analogy with the common zeolite catalysts, deposition of coke on the galloaluminosilicate catalysts also occurs during conversion, such as aromatization, of hydrocarbons at high temperature, thereby lowering the catalytic activity. Generally, material hydrocarbons with larger carbon numbers sustain severer lowering of catalytic activity, and olefins are more apt to generate coke than paraffins, thereby causing a severer lowering of catalytic activity. In fact, in case of aromatization of hydrocarbons on galloaluminosilicate catalysts, using very lower paraffins, such as propane or butane, as raw materials does not lower the catalytic activity so considerably. However, using hydrocarbons containing higher paraffins or olefins as raw materials causes severer lowering of activity, so that it becomes very difficult to maintain the initial high activity for more than 100 hours.
Thus, the reactions easily sustaining the lowering of the activity due to the deposition of coke, such as the above-described aromatization, require frequent regenerations of catalysts for burning the coke at high temperatures. With every regeneration, the catalysts are exposed at high temperatures to the steam generated by the burning of coke, and catalysts with poor wet heat resistance lose their activity considerably with every regeneration, so that a considerable decrease in the catalysts' lifetimes on repeated uses becomes a serious problem from the viewpoint of the process efficiency.
The followings are typical examples of the catalytic conversions of organic compounds that involve the problems as described above.
For example, as to the catalytic cracking of gas oil, it was confirmed that a combined use of zeolites (FCC catalysts) having a pore size of more than 7 angstroms with ZSM-5, which is an MFI type zeolite, improves both the octane number and yield of tile obtained gasoline as compared with the use of the former alone [Japanese Patent Application Kokai Koho (Laid-open) No. 47-8074 {Japanese Patent Application Kokoku Koho (Publication) No. 54-37162}]. However, the ZSM-5 synthesized by the method disclosed therein is so poor in wet heat resistance as to lose its activity considerably with every exposure to an atmosphere of steam during regeneration of the catalyst, with the effects of addition thereof lost rapidly. This catalytic conversion process therefore requires continuous addition of ZSM-5, causing use of a large quantity of ZSM-5.
There is a report that as compared with adding small crystals of ZSM-5, adding large crystals of ZSM-5 to FCC catalysts lessens the lowering of activity caused by steaming [Japanese Patent Application Kokai Koho (Laid-open) No. 60-208395 ]. Nonetheless, the lowering of activity due to the steaming is not yet overcome sufficiently.
In these processes, improving the wet heat resistance of the ZSM-5 would enable addition of the zeolites in a reduced quantity.
There are reported some attempts to improve the wet heat resistance of ZSM-5. For example, in Japanese Patent application Kokai Koho (Laid-open) Nos. 55-51440 and 59-117584 disclosed is that the wet heat resistance of ZSM-5 is improved by introducing metals of Group IB (Cu, Ag), IIB (Zn) or VIII thereto by ion exchange. Nevertheless the improvement is still insufficient, and there arises a problem that the exchanged cations, such as Ag.sup.+, lose their effects on reduction thereof.
There is also known a process of producing aromatic hydrocarbons from hydrocarbons, such as paraffins or olefins (particularly C.sub.5.sup.+ hydrocarbons), by using catalysts containing ZSM-5 [Japanese Patent Application Kokai Koho (Laid-open) No. 49-41322]. In this process, a severe deposition of carbonaceous matters onto the catalysts necessitates frequent regenerations of the catalysts. When the present inventor synthesized the ZSM-5 disclosed in working examples in the specification and used them actually to carry out the same reaction, the catalytic activity was lowered considerably by repeated regenerations by steaming.
It is also reported that zeolites with Ga deposited or ion exchanged thereon exhibit high activity in the above-described aromatization [Japanese Patent Application Kokai Koho (Laid-open) No. 53-92717]. However, there is no teaching how the zeolites were synthesized.
In Japanese patent Application Kokoku Koho (Publication) No. 58-34517 disclosed is a process wherein first gasoline fractions are produced by catalytically cracking a gas oil on cracking catalysts and secondly the ingredients of 4 or less carbon atoms resulting from the cracking and including paraffins and olefins are catalyzed with ZSM-5 to increase the organic content, namely the octane number. The ZSM-5 used were all fresh because of their weakness to wet heat deterioration during regeneration, and the regenerated ZSM-5 were used together with FCC catalysts for the former cracking.
These conventional ZSM-5 are MFI type zeolites. However, as the above-described examples show, although the conventional MFI type zeolites represented by the ZSM-5 are generally effective catalysts or catalyst ingredients for various catalytic conversions of organic compounds, they are so poor in wet heat resistance that there arises a problem that their activity or functions as additive catalysts are easily lowered severely by steaming or by reactions in an atmosphere of steam.
As to the aromatization using galloaluminosilicate catalysts, there have been proposed various techniques. For example, in Japanese Patent Application Kohyo Koho (Laid-open) No. 60-501357 disclosed is increasing the aromatization activity of a galloaluminosilicate by steaming. There is however no description concerning the change of the activity during a long-term steaming (that is, whether the catalytic activity can be maintained sufficiently in spite of the regeneration or repeated regenerations of the catalysts requiring high temperatures and a long-term steaming). Nor is there a description of the variation in the wet heat resistance depending on the preparation methods (synthesizing methods) of the galloaluminosilicate.
In Japanese Patent Application Kokai Koho (laid-open) No. 1-103916 disclosed is obtaining a high yield of of aromatic hydrocarbons from various hydrocarbons by using galloaluminosilicates modified by burning at 700.degree.-1000.degree. C. There is however not described tile change of the activity of the galloaluminosilicates on contact with steam.
That is, these conventional techniques succeeded in providing the galloaluminosilicates exhibiting improved activity in aromatization of hydrocarbons, but are not practical for processes requiring regeneration of catalysts, particularly frequent repetition of reactions and regenerations. The reason is that there is no teaching of the producing methods and compositions that provide galloaluminosilicates having such a high wet heat resistance as to tolerate regeneration or repetition thereof.
It is therefore an important problem to know what producing methods and compositions provide galloaluminosilicates having high catalytic activity and such a high wet heat resistance as to sufficiently tolerate regeneration or repetition thereof.
If galloaluminosilicates having excellent wet heat resistance are found, they will be effective not only for the aromatization of hydrocarbons but also for various reactions catalyzed by other zeolites, such as the ZSM-5. They will be also effective for various processes for catalytic conversion of organic compounds wherein the catalysts necessarily come into contact with steam at high temperature not only during regeneration thereof but also during the reactions (for example, for reactions generating water, such as dehydration of alcohols or hydrogenation of CO, and further for reactions requiring addition of water to material systems).